How SPF works, end to end
Every SPF integration moves through the same five stages. What differs is who performs each one: API clients do this work themselves, while Hosted and on-premise clients have SPF’s own interface do it for them.1
Determine which forms apply
The employee’s home address and one or more work addresses are resolved to taxing jurisdictions, and SPF returns the federal, state, and local withholding forms that apply. In Choose Mode this step is skipped, because the employee selects a form directly.
2
Ask the employee questions
SPF serves each form as a series of question sets (one screen at a time) and tells you which screen comes next based on the answer the employee just gave.
3
Collect the answers
You send the employee’s answers back to SPF, using the question IDs and option values exactly as SPF supplied them.
4
Receive the completed form
SPF returns a completed, signed PDF of the withholding form along with a set of tax parameters: the employee’s withholding elections in a structured, machine-readable form.
5
Store and apply the results
You store the PDF according to your retention obligations and map the tax parameters into your payroll system so the employee is withheld correctly.
Stage five is where SPF hands off. It establishes what the employee’s elections are; turning them into a withholding amount is your payroll engine’s job. See What is SPF for that boundary, and SPF to STE tax parameter mapping if you run both products.
Forms and jurisdictions
Before anything else, it helps to know what SPF means by “a form” and how it decides which ones an employee needs.The form model
Form IDs, names and titles, form types, and how locale variants relate to one another.
Form determination
How addresses resolve to jurisdictions, plus reciprocity, local forms, nexus, and lock-in letters.
Collecting the employee’s answers
SPF drives the employee experience through two separate question systems: one that decides which forms are needed, and one that collects the answers for a given form.Form modes
Choose, Guided, and Single Form mode, and how flow questions differ from form questions.
Question sets and navigation
Why SPF owns the question order, how required conditions work, and how a form reaches its end.
What SPF gives you back
PDFs and tax parameters
The two outputs of a completed form, and how to read tax parameter IDs, values, and value types.
Form versions and effective dates
How SPF versions forms, when a new version takes effect, and why prior versions are retained.
Compliance and language
Penalty of perjury statements
The signature declaration every withholding form requires before it can be submitted.
Languages and locales
English, Spanish, and French support, and why Canadian French forms work differently.
Where to go next
Once these concepts are familiar, pick the quickstart that matches how you’re delivering SPF.API quickstart
Build your own employee-facing interface on the SPF API.
Hosted quickstart
Embed the Symmetry-hosted forms UI in your application.
On-premise quickstart
Run the forms UI inside your own infrastructure.